Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.67	9.652%	$99.4215	$99.42	$99.40	$99.40
Purchase #2	$175.86	3.622%	$182.2296	$182.23	$182.25	$182.20
Purchase #3	$139.80	3.634%	$144.8803	$144.88	$144.90	$144.90
Purchase #4	$119.95	11.151%	$133.3256	$133.33	$133.35	$133.30
Purchase #5	$223.79	10.282%	$246.8001	$246.80	$246.80	$246.80
Purchase #6	$35.65	5.176%	$37.4952	$37.50	$37.50	$37.50
Purchase #7	$159.30	9.481%	$174.4032	$174.40	$174.40	$174.40
7 purchase totals =	$945.02		$1,018.5555	$1,018.56	$1,018.60	$1,018.50